Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $186.72   9.110%   $203.7302   $203.73   $203.75   $203.70  
  Purchase #2 $91.56   5.839%   $96.9062   $96.91   $96.90   $96.90  
  Purchase #3 $226.65   11.187%   $252.0053   $252.01   $252.00   $252.00  
  Purchase #4 $23.26   3.814%   $24.1471   $24.15   $24.15   $24.10  
  Purchase #5 $248.95   10.219%   $274.3902   $274.39   $274.40   $274.40  
  Purchase #6 $44.48   10.571%   $49.182   $49.18   $49.20   $49.20  
  Purchase #7 $68.76   10.234%   $75.7969   $75.80   $75.80   $75.80  
  7 purchase totals = $890.38       $976.1579   $976.17   $976.20   $976.10